In process automation, end users employ several different physical layers. A two-wire twisted pair that transports a 4-20 mA analog signal with a superimposed digital signal at 1,200 bps is the physical layer for HART. The wire pairs in an H1 cable carrying a 31.25 kbps bitstream is the physical layer for FOUNDATION Fieldbus.
Domain-specific concepts like the NAMUR Open Architecture (NOA) or Open Process Automation (OPA) by the Open Process Automation Forum (OPAF) are currently attempting to simplify the construction, commissioning and operation of process plants. Broader use of wireless solutions, simplified field device integration and Ethernet to the field represent integral components of these concepts.
FieldComm Group is one of the industry organizations helping to drive the Advanced Physical Layer (APL) project, which focuses on an extension of the 10BASE-T1L Ethernet physical layer for process automation and instrumentation. Deployable in hazardous areas (Zones 0 and 1, Division 1), APL is based on the same two-wire cable as FOUNDATION Fieldbus H1, thus offering continuity to users.
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